Method and apparatus for low cost error recovery in predictive coding

ABSTRACT

Methods, apparatuses, decoders, and computer programs for replacing decoded parameters in a received multichannel signal are provided. Multichannel parameters of a frame of the signal are decoded. Responsive to a bad frame being indicated, it is determined that a parameter memory is corrupted. Responsive to a bad frame not being indicated: responsive to the parameter memory not being corrupted, a location measure is derived of a reconstructed sound source based on decoded multichannel parameters. Responsive to the parameter memory being corrupted, it is determined, based on the location measure, whether the reconstructed sound source is stable and predominantly concentrated in a subset of channels of multichannels of the received multichannel signal. Responsive to the reconstructed sound source being concentrated in the subset of channels of the multichannels and being stable, parameter recovery is activated to replace decoded multichannel parameters with stored multichannel parameters.

TECHNICAL FIELD

The application relates to methods and apparatuses for error recovery inpredictive coding for stereo or multichannel audio encoding anddecoding.

BACKGROUND

Although the capacity in telecommunication networks is continuouslyincreasing, it is still of great interest to limit the requiredbandwidth per communication channel. In mobile networks smallertransmission bandwidths for each call yields lower power consumption inboth the mobile device and the base station. This translates to energyand cost saving for the mobile operator, while the end user willexperience prolonged battery life and increased talk-time. Further, withless consumed bandwidth per user, the mobile network can service alarger number of users in parallel.

Through modern music playback systems and movie theaters, most listenersare accustomed to high quality immersive audio. In mobiletelecommunication services, the constraints on radio resources andprocessing delay have kept the quality at a lower level and most voiceservices still deliver only monaural sound. Recently, stereo andmulti-channel sound for communication services has gained momentum inthe context of Virtual/Mixed/Augmented Reality which requires immersivesound reproduction beyond mono. To render high quality spatial soundwithin the bandwidth constraints of a telecommunication network stillpresents a challenge. In addition, the sound reproduction also needs tocope with varying channel conditions where occasional data packets maybe lost due to e.g. network congestion or poor cell coverage.

In a typical stereo recording the channel pair may show a high degree ofsimilarity, or correlation. Some embodiments of stereo coding schemesmay exploit this correlation by employing parametric coding, where asingle channel is encoded with high quality and complemented with aparametric description that allows reconstruction of the full stereoimage, such as the scheme discussed in C. Faller, “Parametricmultichannel audio coding: synthesis of coherence cues,” in IEEETransactions on Audio, Speech, and Language Processing, vol. 14, no. 1,pp. 299-310, January 2006. The process of reducing the channel pair intoa single channel is often called a down-mix and the resulting channel isoften called the down-mix channel. The down-mix procedure typicallytries to maintain the energy by aligning inter-channel time differences(ITD) and inter-channel phase differences (IPD) before mixing thechannels. To maintain the energy balance of the input signal, theinter-channel level difference (ILD) may also be measured. The ITD, IPDand ILD may then be encoded and may be used in a reversed up-mixprocedure when reconstructing the stereo channel pair at a decoder. TheITD, IPD, and ILD parameters describe the correlated components of thechannel pair, while a stereo channel pair may also include anon-correlated component which cannot be reconstructed from thedown-mix. This non-correlated component may be represented with aninter-channel coherence parameter (ICC). The non-correlated componentmay be synthesized at a stereo decoder by running the decoded down-mixchannel through a decorrelator filter, which outputs a signal which haslow correlation with the decoded down-mix. The strength of thedecorrelated component may be controlled with the ICC parameter.

Similar principles apply for multichannel audio such as 5.1 and 7.1.4,and spatial audio representations such as Ambisonics or Spatial AudioObject Coding. The number of channels can be reduced by exploiting thecorrelation between the channels and bundling the reduced channel setwith metadata or parameters for channel reconstruction or spatial audiorendering at the decoder.

To overcome the problem of transmission errors and lost packets,telecommunication services make use of Packet Loss Concealment (PLC)techniques. In the case that data packets are lost or corrupted due topoor connection, network congestion, etc., the missing information oflost or corrupt data packets in the receiver side may be substituted bythe decoder with a synthetic signal to conceal the lost or corrupt datapacket. Some embodiments of PLC techniques are often tied closely to thedecoder, where the internal states can be used to produce a signalcontinuation or extrapolation to cover the packet loss. For a multi-modecodec having several operating modes for different signal types, thereare often several PLC technologies that can be implemented to handle theconcealment of the lost or corrupted data packet.

Missing or corrupted packets may be identified by the transport layerhandling the connection and is signaled to the decoder as a “bad frame”through a Bad Frame Indicator (BFI), which may be in the form of a flag.The decoder may store this flag in its internal state and also keeptrack of the history of bad frames, e.g. a “previous bad frameindicator” (PREY BFI). Note that one transmission packet may contain oneor more speech or audio frames. This means that one lost or corruptedpacket will label all the frames contained therein as “bad.”

For stable audio scenes, the parameters may show a high degree ofsimilarity between adjacent frames. To exploit this similarity,predictive coding schemes may be applied. In such a scheme a predictionof the current frame parameters is derived based on the past decodedparameters, and the difference to the true parameters is encoded. Asimple but efficient prediction is to use the last decoded parameters asthe prediction, in which case the predictive coding scheme can bereferred to as a differential encoding scheme.

One issue with the predictive coding schemes is that the schemes can besensitive to errors. For example, if one or more elements of thepredicted sequence are lost, the decoder will have a prediction errorthat may last a long time after the error has occurred. This problem iscalled error propagation and may be present in all predictive codingschemes. An illustration of error propagation is provided in FIG. 1. InFIG. 1, an absolute coding frame is lost before a sequence ofconsecutive predictive coding frames (i.e., a predictive coding streak).The memory, which would have been updated with parameters from the lostframe, will have previous parameters stored and thus be corrupted. Sincethe memory is corrupted by the frame loss, the error will last duringthe entire predictive coding streak and only terminate when a newabsolute coding frame is received. One result of such a loss is theeffect on the synthesized signal, which may be an unwanted and evendrastic change in the perceived location of the source. This isparticularly noticeable if the source has a static and extreme position,e.g. a sound source positioned to either the far right or the far leftin a stereo scene.

One remedy is to force non-predictive coding at regular time intervals,which will terminate the error propagation. Another solution is to use apartial redundancy scheme, where a low-resolution encoding of theparameters is transmitted together with an adjacent audio frame. In casethe decoder detects a frame loss in a predictive coding streak, thelow-resolution parameters can be used to reduce the error propagation.

SUMMARY

One drawback of the above described predictive coding remedies is thatthey consume bandwidth, which is wasted bandwidth when the transmissionchannel is error-free.

According to some embodiments, a method is provided to replace decodedparameters in a received multichannel signal. The method includesdecoding multichannel parameters of a frame of the received multichannelsignal. The method further includes determining whether a bad frame isindicated. Responsive to the bad frame being indicated, the methodincludes determining that a parameter memory is corrupted. The methodincludes responsive to the bad frame not being indicated, and responsiveto the parameter memory not being corrupted, deriving a location measureof a reconstructed sound source based on decoded multichannelparameters. The method includes responsive to the parameter memory beingcorrupted, determining, based on the location measure, whether thereconstructed sound source is stable and predominantly concentrated in asubset of channels of multichannels of the received multichannel signal.Responsive to the reconstructed sound source being concentrated in thesubset of channels of the multichannels and being stable, the methodincludes activating parameter recovery to replace decoded multichannelparameters with stored multichannel parameters.

A potential advantage of using the parameters from memory in place ofdecoded parameters, is that the operations can reduce the problems ofpredictive coding without transmitting redundant parameter informationthat is wasted in error-free channel operation. Moreover, using theestimated parameters only during stable audio scenes avoids the audioscene from becoming “frozen” during unstable audio scenes in anunnatural way.

Another potential advantage of using the parameters from memory in placeof decoded parameters is that the perceived location of the reproducedsound using the parameters from memory can be closer to the actuallocation of the sound compared to the decoded parameters when a badframe has been indicated. In particular, using the parameters frommemory may reduce undesired or unnatural shifts of the location of thesound when the source is stable and concentrated to one channel or asubset of channels.

According to some embodiments of inventive concepts, a decoder for acommunication network is provided. The decoder has a processor andmemory coupled with the processor, wherein the memory comprisesinstructions that when executed by the processor causes the processor toperform operations including decoding multichannel parameters of a frameof a received multichannel signal. The operations further includedetermining whether a bad frame is indicated. The operations furtherinclude responsive to the bad frame being indicated, determining that aparameter memory is corrupted. The operations further include responsiveto the bad frame not being indicated, and responsive to the parametermemory not being corrupted, deriving a location measure of areconstructed sound source based on decoded multichannel parameters. Theoperations further include responsive to the parameter memory beingcorrupted, determining, based on the location measure, whether thereconstructed sound source is stable and predominantly concentrated in asubset of channels of multichannels of the received multichannel signal.Responsive to the reconstructed sound source being concentrated in thesubset of channels of the multichannels and being stable, the operationsinclude activating parameter recovery to replace decoded multichannelparameters with stored multichannel parameters.

According to some embodiments of inventive concepts, a decoderconfigured to operation in a communication network is provided. Thedecoder is adapted to perform operations. The operations includedecoding multichannel parameters of a frame of a received multichannelsignal. The operations include determining whether a bad frame isindicated. The operations include responsive to the bad frame beingindicated, determining that a parameter memory is corrupted. Theoperations include responsive to the bad frame not being indicated, andresponsive to the parameter memory not being corrupted, deriving alocation measure of a reconstructed sound source based on decodedmultichannel parameters. The operations include responsive to theparameter memory being corrupted, determining, based on the locationmeasure, whether the reconstructed sound source is stable andpredominantly concentrated in a subset of channels of multichannels ofthe received multichannel signal. Responsive to the reconstructed soundsource being concentrated in the subset of channels of the multichannelsand being stable, the operations include activating parameter recoveryto replace decoded multichannel parameters with stored multichannelparameters.

According to some embodiments of inventive concepts, a computer programincluding computer-executable instructions that when executed on aprocessor comprised in a device cause the device to perform operationsis provided. The operations include decoding multichannel parameters ofa frame of a received multichannel signal. The operations furtherinclude determining whether a bad frame is indicated. The operationsfurther include responsive to the bad frame being indicated determiningthat a parameter memory is corrupted. The operations include responsiveto the bad frame not being indicated, and responsive to the parametermemory not being corrupted, deriving a location measure of areconstructed sound source based on decoded multichannel parameters. Theoperations include responsive to the parameter memory being corrupted,determining, based on the location measure, whether the reconstructedsound source is stable and predominantly concentrated in a subset ofchannels of multichannels of the received multichannel signal.Responsive to the reconstructed sound source being concentrated in thesubset of channels of the multichannels and being stable, the operationsinclude activating parameter recovery to replace decoded multichannelparameters with stored multichannel parameters.

According to some embodiments of inventive concepts, a computer programcomprising a non-transitory computer-readable storage medium isprovided, the non-transitory computer-readable storage medium havingcomputer-executable instructions that when executed on a processorcomprised in device cause the device to perform operations. Theoperations include decoding multichannel parameters of a frame of areceived multichannel signal. The operations further include determiningwhether a bad frame is indicated. The operations further includeresponsive to the bad frame being indicated, determining that aparameter memory is corrupted. The operations include responsive to thebad frame not being indicated, and responsive to the parameter memorynot being corrupted, deriving a location measure of a reconstructedsound source based on decoded multichannel parameters. The operationsinclude responsive to the parameter memory being corrupted, determining,based on the location measure, whether the reconstructed sound source isstable and predominantly concentrated in a subset of channels ofmultichannels of the received multichannel signal. Responsive to thereconstructed sound source being concentrated in the subset of channelsof the multichannels and being stable, the operations include activatingparameter recovery to replace decoded multichannel parameters withstored multichannel parameters.

According to some embodiments of inventive concepts, an apparatusconfigured to substitute decoded parameters with estimated parameters ina received multichannel signal is provided. The apparatus includes atleast one processor and memory communicatively coupled to the processor,said memory comprising instructions executable by the processor, whichcause the processor to perform operations. The operations includedecoding multichannel parameters of a frame of a received multichannelsignal. The operations further include determining whether a bad frameis indicated. The operations further include responsive to the bad framebeing indicated, determining that a parameter memory is corrupted. Theoperations include responsive to the bad frame not being indicated, andresponsive to the parameter memory not being corrupted, the methodincludes deriving a location measure of a reconstructed sound sourcebased on decoded multichannel parameters. The operations includeresponsive to the parameter memory being corrupted, determining, basedon the location measure, whether the reconstructed sound source isstable and predominantly concentrated in a subset of channels ofmultichannels of the received multichannel signal. Responsive to thereconstructed sound source being concentrated in the subset of channelsof the multichannels and being stable, the operations include activatingparameter recovery to replace decoded multichannel parameters withstored multichannel parameters.

According to other embodiments of inventive concepts, a method isprovided to replace decoded parameters in a received multichannelsignal. The method includes determining whether the coding mode is anabsolute coding mode or a predictive coding mode. The method includesresponsive to the coding mode being a predictive coding mode,determining if a memory corrupted flag is set. The method includesresponsive to the memory corrupted flag being set, determining whether areconstructed sound source is a stable source and a location measure ofthe reconstructed sound source is predominantly concentrated in a subsetof channels. The method includes responsive to the reconstructed soundsource being a stable source and the location measure of thereconstructed sound source being predominantly concentrated in thesubset of channels of the multichannels, substituting decodedmultichannel parameters with stored multichannel parameters. The methodincludes responsive to the memory corrupted flag not being set,analyzing a location measure of a position of the source to update thelocation measure and updating the stored multichannel parameters withthe decoded multichannel parameters.

According to some other embodiments of inventive concepts, a decoder fora communication network is provided. The decoder includes a processorand memory coupled with the processor, wherein the memory comprisesinstructions that when executed by the processor causes the processor toperform operations. The operations include determining whether thecoding mode is an absolute coding mode or a predictive coding mode. Theoperations include responsive to the coding mode being a predictivecoding mode, determining if a memory corrupted flag is set. Theoperations include responsive to the memory corrupted flag being set,determining whether a reconstructed sound source is a stable source anda location measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels. The operations include responsiveto the reconstructed sound source being a stable source and the locationmeasure of the reconstructed sound source being predominantlyconcentrated in the subset of channels of the multichannels,substituting decoded multichannel parameters with stored multichannelparameters. The operations include responsive to the memory corruptedflag not being set, analyzing a location measure of a position of thesource to update the location measure and updating the storedmultichannel parameters with the decoded multichannel parameters.

According to some other embodiments of inventive concepts, a decoderconfigured to operate in a communication network is provided. Thedecoder is adapted to perform operations. The operations includedetermining whether the coding mode is an absolute coding mode or apredictive coding mode. The operations include responsive to the codingmode being a predictive coding mode, determining if a memory corruptedflag is set. The operations include responsive to the memory corruptedflag being set, determining whether a reconstructed sound source is astable source and a location measure of the reconstructed sound sourceis predominantly concentrated in a subset of channels. The operationsinclude responsive to the reconstructed sound source being a stablesource and the location measure of the reconstructed sound source beingpredominantly concentrated in the subset of channels of themultichannels, substituting decoded multichannel parameters with storedmultichannel parameters. The operations include responsive to the memorycorrupted flag not being set, analyzing a location measure of a positionof the source to update the location measure and updating the storedmultichannel parameters with the decoded multichannel parameters.

According to some other embodiments of inventive concepts, a computerprogram comprising computer-executable instructions that when executedon a processor comprised in a device cause the device to performoperations is provided. The operations include determining whether thecoding mode is an absolute coding mode or a predictive coding mode. Theoperations include responsive to the coding mode being a predictivecoding mode, determining if a memory corrupted flag is set. Theoperations include responsive to the memory corrupted flag being set,determining whether a reconstructed sound source is a stable source anda location measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels. The operations include responsiveto the reconstructed sound source being a stable source and the locationmeasure of the reconstructed sound source being predominantlyconcentrated in the subset of channels of the multichannels,substituting decoded multichannel parameters with stored multichannelparameters. The operations include responsive to the memory corruptedflag not being set, analyzing a location measure of a position of thesource to update the location measure and updating the storedmultichannel parameters with the decoded multichannel parameters.

According to some other embodiments of inventive concepts, a computerprogram product comprising a non-transitory computer-readable storagemedium having computer-executable instructions that when executed on aprocessor comprised in device cause the device to perform operations isprovided. The operations include determining whether the coding mode isan absolute coding mode or a predictive coding mode. The operationsinclude responsive to the coding mode being a predictive coding mode,determining if a memory corrupted flag is set. The operations includeresponsive to the memory corrupted flag being set, determining whether areconstructed sound source is a stable source and a location measure ofthe reconstructed sound source is predominantly concentrated in a subsetof channels. The operations include responsive to the reconstructedsound source being a stable source and the location measure of thereconstructed sound source being predominantly concentrated in thesubset of channels of the multichannels, substituting decodedmultichannel parameters with stored multichannel parameters. Theoperations include responsive to the memory corrupted flag not beingset, analyzing a location measure of a position of the source to updatethe location measure and updating the stored multichannel parameterswith the decoded multichannel parameters.

According to some other embodiments of inventive concepts, an apparatusconfigured to substitute decoded parameters with estimated parameters ina received multichannel signal is provided. The apparatus includes atleast one processor and memory communicatively coupled to the processor,said memory comprising instructions executable by the processor, whichcause the processor to perform operations. The operations includedetermining whether the coding mode is an absolute coding mode or apredictive coding mode. The operations include responsive to the codingmode being a predictive coding mode, determining if a memory corruptedflag is set. The operations include responsive to the memory corruptedflag being set, determining whether a reconstructed sound source is astable source and a location measure of the reconstructed sound sourceis predominantly concentrated in a subset of channels. The operationsinclude responsive to the reconstructed sound source being a stablesource and the location measure of the reconstructed sound source beingpredominantly concentrated in the subset of channels of themultichannels, substituting decoded multichannel parameters with storedmultichannel parameters. The operations include responsive to the memorycorrupted flag not being set, analyzing a location measure of a positionof the source to update the location measure and updating the storedmultichannel parameters with the decoded multichannel parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate certain non-limiting embodiments ofinventive concepts. In the drawings:

FIG. 1 is an illustration of error propagation;

FIG. 2 is a block diagram illustrating an example of an environment of adecoder system in which error recovery in predictive coding may beperformed according to some embodiments;

FIG. 3 is a block diagram illustrating components of a stereo encoderand decoder according to some embodiments;

FIG. 4 is a flow chart illustrating operations of a decoder according tosome embodiments of inventive concepts;

FIG. 5 is a block diagram illustrating operations of a decoder accordingto provide error recovery according to some embodiments of inventiveconcepts;

FIG. 6 is a block diagram illustrating a state machine according to someembodiments of inventive concepts;

FIG. 7 is a block diagram illustrating operations to generate substituteparameters according to some embodiments of inventive concepts;

FIG. 8 is a block diagram illustrating a decoder according to someembodiments of inventive concepts; and

FIGS. 9-10 are flow charts illustrating operations of a decoder inaccordance with some embodiments of inventive concepts.

DETAILED DESCRIPTION

Inventive concepts will now be described more fully hereinafter withreference to the accompanying drawings, in which examples of embodimentsof inventive concepts are shown. Inventive concepts may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of present inventive concepts to those skilled inthe art. It should also be noted that these embodiments are not mutuallyexclusive. Components from one embodiment may be tacitly assumed to bepresent/used in another embodiment.

The following description presents various embodiments of the disclosedsubject matter. These embodiments are presented as teaching examples andare not to be construed as limiting the scope of the disclosed subjectmatter. For example, certain details of the described embodiments may bemodified, omitted, or expanded upon without departing from the scope ofthe described subject matter.

The inventive concepts described maintain a memory of the last receivedparameters, corresponding to a source location. If the decoder detectsan error in a predictive coding streak and location analysis confirmsthat the sound source is stable and has an extreme position (i.e., alocation measure of the sound source is predominantly concentrated in asubset of channels of the multichannels of a multichannel signal beingdecoded), the parameters from memory may be used instead of the decodedparameters until the predictive coding streak is terminated by anabsolute coding frame.

In cases where the audio scene is unstable and shows large variation inthe stereo parameters, substituting the decoded parameters with thefrozen estimated parameters may be annoying to the listener.

To achieve these goals, the method in one embodiment includes a locationanalyzer to determine a location of the source, a parameter memory tostore the parameters for the last observed active source, a memorycorruption detector to determine if the parameter memory is corrupt, anda decision mechanism to activate the parameter recovery (replace decodedparameters with parameters stored in memory) based on at least thehistory of the bad frame indicator and in a further embodiment, theoutput of the location analyzer. Here, an active source refers to asource which is intended to be reconstructed, such as the voice in aspeech conversation. When the source is inactive (silent), the capturedsound is typically dominated by background noises which are consideredless relevant for the sound reconstruction. The background noise may becomposed of many different sources which may render an unstable audioscene with large variation in the parametric description. This largevariation should be ignored when estimating the active source location.Hence, it may be beneficial to estimate the location only when thesource is active.

One advantage that may be provided by the inventive concepts includereducing the problems of channel errors during predictive coding withouttransmitting redundant parameter information that is wasted inerror-free channel operation. Another advantage that may be provided isthat parameter estimation in predictive decoding operations is notenabled for unstable audio scenes, which may result in avoiding audioscenes that are unnaturally frozen. Yet another advantage that may beprovided is that it may reduce unnatural or unwanted instabilities inthe location of a source when the source location is stable andconcentrated to a subset of the channels of a multi-channel signal.

FIG. 2 illustrates an example of an operating environment of a decoder200 that may be used to decode multichannel bitstreams as describedherein. The decoder 200 may be part of a media player, a mobile device,a set-top device, a desktop computer, and the like. In otherembodiments, the decoder 200 may be embodied in the hardware and/orsoftware of a standalone server, a cloud-implemented server, adistributed server or as processing resources in a server farm. Forexample, the decoder may be part of a cloud-implemented teleconferenceapplication. The decoder 200 receives encoded bitstreams transmitted viaa transport layer of a network. The bitstreams may be sent from anencoder, from a storage device 204, from a device on the cloud vianetwork 202, etc. During operation, decoder 200 receives and processesthe frames of the bitstream as described herein. The decoder 200 outputsmulti-channel audio signals and may transmit the multi-channel audiosignals to a multi-channel audio player 206 having at least oneloudspeaker for playback of the multi-channel audio signals. Storagedevice 204 may be part of a storage depository of multi-channel audiosignals such as a storage repository of a store or a streaming musicservice, a separate storage component, a component of a mobile device,etc. Multichannel audio player may be a Bluetooth speaker, a devicehaving at least one loudspeaker, a mobile device, a streaming musicservice, etc.

While the parametric stereo reproduction gives good quality at lowbitrates, the quality tends to saturate for increasing bitrates due tothe limitation of the parametric model. To overcome this issue, thenon-correlated component can be encoded. This encoding is achieved bysimulating the stereo reconstruction in the encoder and subtracting thereconstructed signal from the input channel, producing a residualsignal. If the down-mix transformation is revertible, the residualsignal can be represented by only a single channel for the stereochannel case. Typically, the residual signal encoding is targeted to thelower frequencies which are psycho-acoustically more relevant while thehigher frequencies can be synthesized with the decorrelator method. FIG.3 is a block diagram depicting an embodiment of a setup for a parametricstereo codec including a residual coder. In FIG. 3, the encoder 310 mayreceive input signals, perform the processing described above in thestereo processing and down-mix block 312, encode the output via down-mixencoder 314, encode the residual signal via residual encoder 316, andencode the ITD, IPD, ILD, and ICC parameters via parameter encoder 318.The decoder 320 may receive the encoded output, the encoded residualsignal, and the encoded parameters. The decoder 320 may decode theresidual signal via residual decoder 326 and decode the down-mix signalvia down-mix decoder 324. The parameter decoder 328 may decode theencoded parameters. The stereo synthesizer 322 may receive the decodedoutput signal and the decoded residual signal and based on the decodeparameters, output stereo channels CH1 and CH2.

FIG. 8 is a block diagram illustrating elements of decoder 200configured to decode multi-channel audio frames and provide errorrecovery for lost or corrupt frames in predictive coding mode accordingto some embodiments of inventive concepts. As shown, decoder 200 mayinclude a network interface circuit 805 (also referred to as a networkinterface) configured to provide communications with otherdevices/entities/functions/etc. The decoder 200 may also include aprocessor circuit 801 (also referred to as a processor) coupled to thenetwork interface circuit 805, and a memory circuit 803 (also referredto as memory) coupled to the processor circuit. The memory circuit 803may include computer readable program code that when executed by theprocessor circuit 801 causes the processor circuit to perform operationsaccording to embodiments disclosed herein.

According to other embodiments, processor circuitry 801 may be definedto include memory so that a separate memory circuit is not required. Asdiscussed herein, operations of the decoder 200 may be performed byprocessing circuitry 801 (also referred to as processor) and/or networkinterface circuitry 805 (also referred to as a network interface). Forexample, processing circuitry 801 may control network interface 805 totransmit communications to multichannel audio players 206 and/or toreceive communications through network interface 805 from one or moreother network nodes/entities/servers such as encoder nodes, depositoryservers, etc. Moreover, modules may be stored in memory circuitry 803,and these modules may provide instructions so that when instructions ofa module are executed by processing circuitry 801, processing circuitry801 performs respective operations.

In the description that follows, the stereo decoder of a stereo encoderand decoder system as outlined in FIG. 3 may be used. Two channels willbe used to describe the embodiments. These embodiments may be used withmore than two channels. The multi-channel encoder 310 may process theinput left and right channels in segments referred to as frames. Thestereo analysis and down-mix block 312 may conduct a parametric analysisand produce a down-mix. For a given frame m the two input channels maybe written

$\quad\left\{ \begin{matrix}{l\left( {m,n} \right)} \\{r\left( {m,n} \right)}\end{matrix} \right.$

where l denotes the left channel, r denotes the right channel, n=0, 1,2, . . . , N denotes the sample number in frame m and N is the length ofthe frame. In an embodiment, the frames may be extracted with an overlapin the encoder such that the decoder may reconstruct the multi-channelaudio signals using an overlap add strategy. The input channels may bewindowed with a suitable windowing function w(n) and transformed to theDiscrete Fourier Transform (DFT) domain

$\quad\left\{ \begin{matrix}{{X_{L}\left( {m,k} \right)} = {\sum\limits_{n = 0}^{N - 1}{{l\left( {m,n} \right)}{w(n)}e^{- \frac{j2\pi kn}{N}}}}} \\{{X_{R}\left( {m,k} \right)} = {\sum\limits_{n = 0}^{N - 1}{{r\left( {m,n} \right)}{w(n)}e^{- \frac{j2\pi kn}{N}}}}}\end{matrix} \right.$

Note that other frequency domain representations may be used here, suchas a Quadrature Mirror Filter (QMF) filter bank, a Hybrid QMF filterbank or an odd DFT (ODFT) representation which is composed of the MDCT(modified discrete cosine transform) and MDST (modified discrete cosinetransform) transform components.

For the parametric analysis, the frequency spectrum may be partitionedinto bands b, where each band b corresponds to a range of frequencycoefficients

k=k _(start(b)) . . . k _(end(b)) ,b=0,1,2, . . . N _(bands)−1

where N_(bands) denote the total number of bands. The band limits aretypically set to reflect the resolution of the human auditory perceptionwhich suggests narrow bands for low frequencies and wider bands for highfrequencies. Note that different band resolution may be used fordifferent parameters.

The signals may then be analyzed to extract the ITD, IPD and ILDparameters. Note that the ILD may have a significant impact on theperceived location of a sound. In some embodiments, it may be thereforecritical to reconstruct the ILD parameter with high accuracy to maintaina stable and correct location of the sound.

In addition, the channel coherence may be analyzed, and an ICC parametermay be derived. The set of multi-channel audio parameters for frame mmay contain the complete set of ITD, IPD, ILD and ICC parameters used inthe parametric representation. The parameters may be encoded by aparameter encoder 318 and added to the bitstream to be stored and/ortransmitted to a decoder.

Before producing a down-mix channel, in one embodiment, it may bebeneficial to compensate for the ITD and IPD to reduce the cancellationand maximize the energy of the down-mix. The ITD compensation may beimplemented both in time domain before the frequency transform or infrequency domain, but it essentially performs a time shift on one orboth channels to eliminate the ITD. The phase alignment may beimplemented in different ways, but the purpose is to align the phasesuch that the cancellation is minimized. This ensures maximum energy inthe down-mix. The ITD and IPD adjustments may be done in frequency bandsor be done on the full frequency spectrum and the adjustments may bedone using the quantized ITD and IPD parameters to ensure that themodification can be inverted in the decoder stage.

The embodiments described below are independent of the realization ofthe IPD and ITD parameter analysis and compensation. In other words, theembodiments are not dependent on how the IPD and ITP are analyzed orcompensated. In such embodiments, the ITD and IPD adjusted channels maybe denoted with an apostrophe (′):

$\quad\left\{ \begin{matrix}{X_{L}^{\prime}\left( {m,k} \right)} \\{X_{R}^{\prime}\left( {m,k} \right)}\end{matrix} \right.$

The ITD and IPD adjusted input channels may then be down-mixed by theparametric analysis and down-mix block 312 to produce a mid/siderepresentation, also called a down-mix/side representation. One way toperform the down-mix is to use the sum and difference of the signals:

$\quad\left\{ \begin{matrix}{{X_{M}\left( {m,k} \right)} = \frac{{X_{L}^{\prime}\left( {m,k} \right)} + {X_{R}^{\prime}\left( {m,k} \right)}}{2}} \\{{X_{S}\left( {m,k} \right)} = \frac{{X_{L}^{\prime}\left( {m,k} \right)} - {X_{R}^{\prime}\left( {m,k} \right)}}{2}}\end{matrix} \right.$

The down-mix signal X_(M)(m, k) may be encoded by down-mix encoder 314to be stored and/or transmitted to a decoder. This encoding may be donein frequency domain, but it may also be done in time domain. In thelatter case a DFT synthesis stage is required to produce a time domainversion of the down-mix signal, which is in turn provided to thedown-mix encoder 314. The transformation to time domain may, however,introduce a delay misalignment with the multi-channel audio parametersthat would require additional handling. In one embodiment, this delaymisalignment is solved by introducing additional delay or byinterpolating the parameters to ensure that the decoder synthesis of thedown-mix and the multi-channel audio parameters are aligned.

The reconstruction of the side signal X_(S)(m, k) may be generated fromthe down-mix and the obtained multi-channel audio parameters through alocal parametric synthesis. A side signal predictionX_({tilde over (S)})(m, k) can be derived using the down-mix signal

X _({tilde over (S)})(m,k)=p(X _(M)(m,k))

where p(·) is a predictor function and may be implemented as a singlescaling factor α which minimizes the mean squared error (MSE) betweenthe side signal and the predicted side signal. Further, the predictionmay be applied on frequency bands and involve a prediction parameter foreach frequency band b.

X _({tilde over (S)})(m,k)=α_(b) X _(M)(m,k),k=k _(start(b)) . . . k_(end(b))

If the coefficients of band b are designated as column vectorsX_({tilde over (S)},b)(m) and X_(M,b)(m), the minimum MSE predictor canbe derived as

$\alpha_{b} = \frac{{X_{M,b}(m)}^{T}{X_{S,b}(m)}}{{X_{M,b}(m)}^{T}{X_{M,b}(m)}}$

However, this expression may be simplified to produce a more stableprediction parameter. Although the prediction parameter α_(b) does notrepresent a level difference, it may control the portion of the down-mixsignal which is routed to the left and right channels. Hence, as for theILD parameter, the prediction parameter α_(b) (m) may have a significantimpact on the perceived sound location. Further details are described inthe prediction mode of Breebaart, J., Herre, J., Faller, C., Rödén, J.,Myburg, F., Disch, S., . . . & Oomen, W. (2005). “MPEG spatial audiocoding/MPEG surround: Overview and current status,” 2005 In Preprint119th Cony. Aud. Eng. Soc. (No. LCAV-CONF-2005-029). The predictionparameter α_(b) (m) is in turn encoded using an inter-frame predictivecoding scheme, where differences between the frames m are considered.For each band b a difference from the reconstructed parameters â_(b) (m)of the previous frame may be calculated

Δα_(b)(m)=α_(b)(m)−â _(b)(m−1)

The encoder may choose to encode either α_(b)(m) or Δα_(b)(m), dependingon which of them yields the lowest bit consumption. In an embodiment,α_(b)(m) and Δα_(b)(m) may be quantized using a scalar quantizerfollowed by an entropy coder on the quantizer indices. Arithmeticcoding, Huffman coding and Golomb-Rice coding are examples of codingwhich may be used as an entropy coder. The entropy coder would assignsmaller code words to small variations, i.e. small values of Δα_(b)(m).This means that the predictive coding using Δα_(b)(m) is likely to beused for stable audio scenes. For fast scene changes, resulting in largeΔα_(b)(m), the bit consumption for the encoding of α_(b)(m) may be lowerby using a non-predictive, or absolute encoding scheme. The encodingscheme thus may have two modes:

1) ABSOLUTE: encoding of α_(b)(m), and

2) PREDICTIVE: encoding of Δα_(b)(m).

The encoding mode α_(mode)(m)∈{ABSOLUTE, PREDICTIVE} would need to beencoded for each frame m, such that the decoder knows if the encodedvalue is

1) ABSOLUTE: {circumflex over (α)}_(b)(m), or

2) PREDICTIVE: Δ{circumflex over (α)}_(b)(m).

Further variations of this encoding scheme are possible. For instance,if the prediction parameter α_(b)(m) shows high correlation with anotherparameter, such as the residual coding energy or a correspondingrepresentation, it may be beneficial to encode those parameters jointly.The important part is that when the encoding scheme has a predictivecoding mode and an absolute (non-predictive) coding mode, that thisdecision is encoded and signaled to the decoder. A sequence ofconsecutive PREDICTIVE coding modes may be referred to as a “predictivecoding streak” or “predictive streak” and would be observed for audiosegments where the scene is stable. If an audio frame in the onset ofthe predictive streak is lost, the parameters may suffer from errorpropagation during the entire streak (see FIG. 1). To reduce the effectof error propagation, ABSOLUTE coding may be forced at regularintervals, which effectively limits the predictive streak to a maximumlength in time.

After encoding, a local reconstruction of the parameter {circumflex over(α)}_(b)(m) is derived in the encoder and stored in memory to be usedwhen encoding the next frame.

{circumflex over (α)}_(b,mem):={circumflex over (α)}_(b)(m)

The decoding steps may be similar to the encoder steps. In the decoder:

${{\overset{\hat{}}{\alpha}}_{b}(m)} = \left\{ \begin{matrix}{{{\overset{\hat{}}{\alpha}}_{b}(m)},} & {{\alpha_{mode}(m)} = {ABSOLUTE}} \\{{{\Delta{{\overset{\hat{}}{\alpha}}_{b}(m)}} + {\overset{\hat{}}{\alpha}}_{b,{mem}}},} & {{\alpha_{mode}(m)} = {PREDICTIVE}}\end{matrix} \right.$

While the predictive coding is described for the reconstructed values,it should be noted that it is also possible to conduct the predictivecoding step on the quantizer indices. The principle of memory dependencyhowever remains the same.

During error-free operation the local reconstruction in the encoder isidentical to the reconstructed parameter {circumflex over (α)}_(b)(m) inthe decoder. Note also that the memory {circumflex over (α)}_(b,mem)will be identical to reconstructed parameter values for frame m−1,{circumflex over (α)}_(b)(m−1). For the very first frame, the parametermemory may be set to some predefined value, e.g. all zeroes or theaverage expected value of the parameter.

Details on residual coding shall now be discussed. Given the predictedside signal, a prediction residual X_(R)(m,k) can be created.

X _(R)(m,k)=X _(S)(m,k)−X _({tilde over (S)})(m,k)

The prediction residual may be inputted into a residual encoder 316. Theencoding may be done directly in DFT domain or it may be done in timedomain. Similarly, as for the down-mix encoder, a time domain encoderwould require a DFT synthesis which may require alignment of the signalsin the decoder. The residual signal represents the diffuse componentwhich is not correlated with the down-mix signal. If a residual signalis not transmitted, a solution in one embodiment may be to substitute asignal for the residual signal in the stereo synthesis state in thedecoder with the signal coming from a decorrelated version of thedecoded down-mix signal. The substitute is typically used for lowbitrates where the bit budget is too low to represent the residualsignal with any useful resolution. For intermediate bit rates, it may becommon to encode a part of the residual. In this case the lowerfrequencies are often encoded, since they may be perceptually morerelevant. For the remaining part of the spectrum, the decorrelatorsignal may be used as a substitute for the residual signal in thedecoder. This approach is often referred to as a hybrid coding mode.Further details are provided in the decoder description below.

The representation of the encoded down-mix, the encoded multi-channelaudio parameters, and the encoded residual signal may be multiplexedinto a bitstream (not shown), which may be transmitted to a decoder 320or stored in a medium for future decoding.

Within the decoder, a down-mix decoder 328 may provide a reconstructeddown-mix signal {circumflex over (M)}(m,n) which is segmented into DFTanalysis frames m and n=0, 1, 2, . . . , N−1 denote the sample numberswithin frame m. The analysis frames are typically extracted with anoverlap which permits an overlap-add strategy in the DFT synthesisstage. The corresponding DFT spectra may be obtained through a DFTtransform

${X_{\hat{M}}\left( {m,k} \right)} = {\sum\limits_{n = 0}^{N - 1}{{\overset{\hat{}}{M}\left( {m,n} \right)}{w(n)}e^{- \frac{j2\pi kn}{N}}}}$

where w(n) denotes a suitable windowing function. The shape of thewindowing function can be designed using a trade-off between frequencycharacteristics and algorithmic delay due to length of the overlappingregions. Similarly, a residual decoder 326 produces a reconstructedresidual signal {circumflex over (R)}(m,n) for frame m and timeinstances n=0, 1, 2, . . . N_(R)−1. Note that the frame length N_(R) maybe different from N since the residual signal may be produced at adifferent sampling rate. Since the residual coding may be targeted onlyfor the lower frequency range, it may be beneficial to represent it witha lower sampling rate to save memory and computational complexity. A DFTrepresentation of the residual signal X_({circumflex over (R)})(m,k) isobtained. Note that if the residual signal is upsampled in DFT domain tothe same sampling rate as the reconstructed down-mix, the DFTcoefficients will need to be scaled with N/N_(R) and theX_({circumflex over (R)})(m,k) would be zero-padded to match the lengthN. To simplify the notation, and since the embodiments are not affectedby the use of different sampling rates, for purposes of betterunderstanding, the sampling rates shall be equal and N_(R)=N in thefollowing description. Thus, no scaling or zero-padding shall be shown.

It should be noted that the frequency transform by means of a DFT is notnecessary in case the down-mix and/or the residual signal is encoded inDFT domain. In this case, the decoding of the down-mix and/or residualsignal provides the DFT spectrum that are necessary for furtherprocessing.

In an error free frame, often referred to as a good frame, themulti-channel audio decoder may produce the multi-channel synthesisusing the decoded down-mix signal together with the decodedmulti-channel audio parameters in combination with the decoded residualsignal. For the case of the prediction parameter α_(b)(m) the decodermay use the mode parameter α_(mode)(m) to select the appropriatedecoding mode and produces the reconstructed prediction parameterα_(b)(m),

${{\overset{\hat{}}{\alpha}}_{b}(m)} = \left\{ \begin{matrix}{{{\overset{\hat{}}{\alpha}}_{b}(m)},} & {{\alpha_{mode}(m)} = {ABSOLUTE}} \\{{{\Delta{{\overset{\hat{}}{\alpha}}_{b}(m)}} + {\overset{\hat{}}{\alpha}}_{b,{mem}}},} & {{\alpha_{mode}(m)} = {PREDICTIVE}}\end{matrix} \right.$

The parameter memory is updated with the reconstructed predictionparameter {circumflex over (α)}_(b)(m).

{circumflex over (α)}_(b,mem):={circumflex over (α)}_(b)(m)

The decoded down-mix X_({circumflex over (M)})(m,k), the stereoparameters and the residual signal X_({circumflex over (R)})(m,k) arefed to the parametric stereo synthesis block 322 to produce thereconstructed stereo signal. After the stereo synthesis in DFT domainhas been applied, the left and right channels are transformed to timedomain and output from the stereo decoder.

In case the decoder detects a lost or corrupted frame, the decoder mayuse one or several PLC modules to conceal the missing data. There may beseveral dedicated PLC technologies to substitute the missinginformation, e.g. as part of the down-mix decoder, residual decoder orthe parameter decoder. The goal of the PLC is to generate anextrapolated audio segment that is similar to the missing audio segment,and to ensure smooth transitions between the correctly decoded audiobefore and after the lost or corrupted frame.

The PLC method for the stereo parameters may vary. An example is tosimply repeat the parameters of the previously decoded frame. Anothermethod is to use the average stereo parameters observed for a largeaudio database, or to slowly converge to the average stereo parametersfor consecutive frame losses (burst losses). The PLC method may updatethe parameter memory with the concealment parameters, or it may leavethe parameter memory untouched such that the last decoded parametersremain. In any case, the memory will be out-of-synch with respect to theencoder.

Turning to FIG. 4, a flow-chart of the decoder operation in anembodiment of predictive parametric coding recovery is provided. If abad frame is indicated through the Bad Frame Indicator (BFI) atoperation 400, the decoder may employ packet loss concealment methods atoperation 402 and in some embodiments, may set a flag for indicatingcorruption in memory of decoded parameters in operation 404 (e.g.,α_(memory_corrupted_flag):=TRUE). If the BFI is not active, normaldecoding is used in operation 406. After the normal decoding, theparameter recovery operation 408 is run.

In more detail, the error-free decoding operations may be described asoutlined by FIG. 5. FIG. 5 may be compared to the stereo decoder block320 of FIG. 3. FIG. 5 provides a down-mix decoder 510 and optionally aresidual decoder 520. The decoder has a parameter decoder with parameterrecovery 530 that is described in more detail below.

The parameter decoder 532 may perform decoding of the stereo parametersusing either an absolute coding mode or a predictive coding mode. In thedescription below, a reconstructed side signal prediction parameter{circumflex over (α)}_(b) (m) shall be used for the error recoverymethod. In the location analyzer block 538, a location measure, whichexpresses the position of the source, is derived. An example of alocation measure is to use the mean α(m) of the reconstructed predictionparameter â_(b) (m) over all sub-bands for each frame.

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{\overset{\hat{}}{\alpha}}_{b}(m)}}}$

The recovery solution is to be activated when the position is extremeand static (or stable). The extreme position may be manifested as aconcentration of signal power to a certain channel or direction, where ashift in the direction of the concentrated energy has a large impact onthe perceived position. For example, in a stereo signal, the extremeposition represents a source concentrated in either the left or theright channel. In other words, the location measure of the source (e.g.,reconstructed source signal) is predominantly concentrated in a subsetof the channels of the multichannels. For a stereo signal, the locationmeasure of the source would be predominantly concentrated in one of thetwo channels. An activation mechanism may be based on a low-passfiltered position, e.g.

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

Here, any position value below the threshold ā_(THR) will reset α_(LP)(m) to zero.

A suitable value for the filter parameter γ may be γ=0.425 or be in therange [0.3,0.7]. An extreme location decision P(m) may be formed bycomparing the low-pass filtered position to a fixed threshold,

${P(m)} = \left\{ \begin{matrix}{1,} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where ā_(THR) depends on the range of the parameter α. Here, the rangefor α_(b), consequently α, is [−1.0,1.0] and suitable value for α _(THR)is 0.4. In other words, a P(m) equal to 1 indicates that the soundsource is a stable source which is panned either to left or rightchannel and thus is at an extreme position. Thus, with the α _(THR)value being 0.4, any value of α _(LP)(m) being above 0.4 or below −0.4(i.e., |α _(LP)(m)|>0.4) would indicate that the sound source is at anextreme position (e.g., the location measure is predominantlyconcentrated in either the left channel or the right channel). The valuefor α _(THR) may be set to other values.

The location measure described above provides a solution that is acomputationally simple implementation. However, it may make sense from aperceptual perspective to include a weighting of the parameterdifferences which takes the band energy of the down-mix into account.Furthermore, the weighting coefficients can be normalized to [0.0, 1.0]range so that α remains in the range of [−0.1, 0.1]. Therefore, analternative expression for the location may be:

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{{\overset{\hat{}}{\alpha}}_{b}(m)} \cdot {{\overset{˜}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum\limits_{k = k_{{start}{(b)}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{˜}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where α _(w)(m) is the weighted location measure, which comprises aweighted mean of a reconstructed prediction parameter {circumflex over(α)}_(b) (m) over all sub-bands for each frame m and N_(bands) is anumber of sub-bands in frame m, w_(b) (m) and {tilde over (w)}_(b) (m)are weighting coefficients, k_(end(b)) is an end of a number of sums,k_(start(b)) is a start of the number of sums andX_({circumflex over (M)})(m, k) is a transformed down-mix signal.

The above expression emphasizes the high energy bands in the panningmeasure α(m). With applying weighting to α, there might be a need ofre-optimizing the filter parameter γ. It may further be desirable toupdate the location measure only during frames that are classified ascoming from an active source, or to normalize the weighting with anestimate of the current peak energy or noise floor level.

The recovery decision logic depends on outputs from memory corruptiondetector 536 and location analyzer 538. The memory corruption detector536 may use at least the coding mode of parameters (predictive/absolute)and the bad frame indicator (BFI) in the detection of memory corruption.The recovery decision logic can be further described by a state machineas outlined in FIG. 6.

Turning to FIG. 6, the starting state 610 represents the normal decodingmode. In case the decoder is in a predictive mode α_(mode)=PREDICTIVEand, the previous frame was a bad frame which technically means thememory of the parameters {circumflex over (α)}_(b,mem) is corrupted(α_(memory_corrupted_flag):=TRUE) and the audio has an extreme andstable position (|α _(LP)(m)|≥α _(THR)), the recovery state 620 isentered. If, while in the recovery state 620, the decoder enters into anabsolute decoding mode α_(mode)=ABSOLUTE, the normal decoding state 610is entered.

In the recovery state 620, the decoded parameters are substituted withthe parameters stored in memory:

{circumflex over (α)}_(b)(m):={circumflex over (α)}_(b,mem)

Since the parameters {circumflex over (α)}_(b)(m) are now from memory,it may be preferable to not update the parameter memory and positionmeasure. Effectively, this means α _(LP)(m)=α _(LP)(m−1).

Returning to FIG. 5, the output of the parameter decoder with parameterrecovery block 530 is input to the stereo synthesizer block 540 togetherwith the output of the down-mix decoder block 510 and potentially theresidual decoder block 520 for the stereo synthesizer block 540 tosynthesize audio signals to output on channels CH1 and/or CH2.

The operation of parameter recovery can also be described by theflow-chart of FIG. 7. Turning now to FIG. 7, in operation 710, theα_(mode) (m) parameter may be checked to determine if the coding mode isabsolute or predictive.

Responsive to the coding mode being an absolute coding mode, inoperation 720, the flag for indicating memory corruption may be unsete.g., α_(memory_corrupted_flag):=FALSE.

Responsive to the coding mode being a predictive coding mode, inoperation 730, the memory status may be checked. If the parameter memoryis not corrupted (e.g., α_(memory_corrupted_flag)=FALSE), the locationof the sound source may be analyzed in operation 740. That is, α_(LP)(m) may be updated.

In operation 750, the memory of decoded parameters may be updated.Responsive to the parameter memory being corrupted (e.g.,α_(memory_corrupted_flag)=TRUE), in operation 760, a determination ismade as to whether or not the sound source is a stable source with anextreme position (e.g., |α _(LP)(m)|>α _(THR) indicating the locationmeasure is predominantly concentrated in a subset of channels of themultichannel system).

In operation 770, responsive to the sound source being a stable sourcewith an extreme position, decoded parameters are substituted with thememory of decoded parameters.

The operation of the decoder with parameter recovery can also bedescribed by the flow-chart in FIG. 9. In operation 900 the processingcircuitry 801 of decoder 200 may decode multichannel parameters of aframe of the received multichannel signal. This operation may be similarto operation 406 of FIG. 4. In operation 902, the decoder 200 maydetermine whether a bad frame is indicated. This operation may besimilar to operation 400 of FIG. 4. In one embodiment, this may be aflag derived from a flag in a data packet message.

Responsive to the bad frame being indicated, the processing circuitry801 may perform packet loss concealment operations in operation 904.This operation may be similar to operation 402 of FIG. 4. For example,the packet loss concealment operations described above with respect toFIG. 3 may be performed in operation 904.

In operation 906, the processing circuitry 801 may determine, based onat least a coding mode and a previous bad frame indicator, whether aparameter memory is corrupted. This operation may be similar tooperation 730 of FIG. 7. In one embodiment, the coding mode may be oneof an absolute coding mode or a predictive coding mode. In thisembodiment, the determining is based on the coding mode being thepredictive coding mode. Thus, determining, based on at least a codingmode and a previous bad frame indicator, whether a parameter memory iscorrupted is determined based on the coding mode being the predictivecoding mode and the previous bad frame indicator.

In operation 908, the processing circuitry 801 may derive a locationmeasure of a position of the source based on decoded multichannelparameters. This operation may be similar to operation 740 of FIG. 7. Inone embodiment, the location measure may be derived based on

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{\overset{\hat{}}{\alpha}}_{b}(m)}}}$

where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub bands inframe m.

In other embodiments, the location measure may be derived based on

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{{\overset{\hat{}}{\alpha}}_{b}(m)} \cdot {{\overset{˜}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum\limits_{k = k_{{start}{(b)}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{˜}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m, w_(b)(m) and {tilde over (w)}_(b)(m) are weightingcoefficients, k_(end(b)) is an end of a number of sums, k_(start(b)) isa start of the number of sums and X_({circumflex over (M)})(m, k) is atransformed down-mix signal.

In operation 910, the processing circuitry 801 may determine, whetherthe reconstructed sound source is stable and the location measure ispredominantly concentrated in a subset of channels of the multichannelsof the received multichannel signal. This operation may be similar tooperation 760 of FIG. 7. In one embodiment, determining whether thereconstructed sound source is stable and the location measure ispredominantly concentrated in a subset of channels of the multichannelsincludes determining whether the low-pass filtered position is above athreshold and responsive to the low-pass filtered position being abovethe threshold, determining that the location measure is predominantlyconcentrated in a subset of channels of the multichannels. The low-passfiltered position may be determined based on

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where γ is a filter parameter, α(m) is a mean of a reconstructedprediction parameter for frame m and α _(LP)(m) is the low-pass filteredposition.

When the multichannels are two channels (e.g., a stereo system with leftand right channels), the determining whether the location measure ispredominantly concentrated in a subset of channels of multichannels ofthe received multichannel signal includes determining whether thelocation measure is predominantly concentrated in one of the twochannels.

In operation 912, the processing circuitry 801 may, responsive to thelocation measure of the reconstructed sound source being concentrated inthe subset of channels of the multichannels and the reconstructed soundsource being stable and the parameter memory being corrupted, activateparameter recovery to replace decoded multichannel parameters withstored multichannel parameters. This operation may be similar tooperation 770 of FIG. 7.

The operation of the decoder with parameter recovery can also be furtherdescribed by the flow-chart in FIG. 10.

When a bad frame is indicated, one or more PLC methods are used todetermine parameters. The bad frame may by indicated by a BFI flag thatsignals that a bad frame has been received. In operation 1000, theprocessing circuitry 801 may, responsive to a bad frame being indicated,set a memory corrupted flag to indicate that the memory of theparameters is corrupted.

When a bad frame is not indicated, parameter decoder operation withparameter recovery is used. In operation 1002, the processing circuitry801 of decoder 200 may determine whether the coding mode is an absolutedecoding mode or a predictive coding mode. The decoder 200 may receivethe coding mode from the encoder. This operation may be similar tooperation 710 of FIG. 7.

Responsive to coding mode being in an absolute coding mode, theprocessing circuitry 801 in operation 1004 unsets a memory corruptedflag. The memory corrupted flag may be used to indicate that the memoryof the parameters is corrupted. This can occur when the previous frameto a frame currently being decoded was a bad frame, which means that thememory of the parameters is corrupted. An example of setting a memorycorrupted flag is also illustrated in FIG. 4.

Responsive to the coding mode being in a predictive coding mode, theprocessing circuitry 801 in operation 1006 may determine if the memorycorrupted flag is set. This operation may be similar to operation 730 ofFIG. 7.

Responsive to the memory corrupted flag being set, the processingcircuitry 801 in operation 1008 may determine whether a reconstructedsound source is a stable sound source and a location measure of thereconstructed sound source is predominantly concentrated in a subset ofchannels of a multichannel signal being decoded. This operation may besimilar to operation 760 of FIG. 7. In one embodiment, this determiningwhether the location measure of the reconstructed sound source ispredominantly concentrated in the subset of channels includesdetermining whether the absolute value of a low-pass filtered positionis above a threshold and responsive to the absolute value of thelow-pass filtered position being above the threshold, determining thatthe location measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels. The low-pass filtered position maybe determined based on

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where γ is a filter parameter, α(m) is a mean of a reconstructedprediction parameter for frame m and α_(LP)(m) is the low-pass filteredposition.

When the multichannels are two channels (e.g., a stereo system with leftand right channels), the determining whether the location measure of thereconstructed sound source is predominantly concentrated in a subset ofchannels includes determining whether the location measure of thereconstructed sound source is predominantly concentrated in one of thetwo channels.

In operation 1010, the processing circuitry 801 may, responsive to thereconstructed sound source being a stable source and the locationmeasure of the reconstructed sound source being predominantlyconcentrated in the subset of channels of the multichannels, substitutedecoded multichannel parameters with stored multichannel parameters.This operation may be similar to operation 770 of FIG. 7.

Responsive to the memory corrupted flag not being set, the processingcircuitry 801 may analyze a location measure of a position of the sourceto update the location measure in operation 1012. This operation may besimilar to operation 740 of FIG. 7. In one embodiment, updating thelocation measure may be updating the location measure based on

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{\overset{\hat{}}{\alpha}}_{b}(m)}}}$

where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub bands inframe m.

In other embodiments, updating the location measure may be updating thelocation measure based on

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{{\overset{\hat{}}{\alpha}}_{b}(m)} \cdot {{\overset{˜}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum\limits_{k = k_{{start}{(b)}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{˜}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter α_(b)(m) over all sub-bands for eachframe m and N_(bands) is a number of sub-bands in frame m, w_(b)(m) and{tilde over (w)}_(b)(m) are weighting coefficients, k_(end(b)) is an endof a number of sums, k_(start(b)) is a start of the number of sums andX_({circumflex over (M)})(m, k) is a transformed down-mix signal.

Responsive to the memory corrupted flag not being set, the processingcircuitry 801 in operation 1014 may update the stored multichannelparameters with the decoded multichannel parameters. This operation maybe similar to operation 750 of FIG. 7.

The description above describes the parameter recovery using the decoder200. A potential advantage of using the parameters from memory in placeof decoded parameters, is that the operations can reduce the problems ofpredictive coding without transmitting redundant parameter informationthat is wasted in error-free channel operation. Moreover, using theestimated parameters only during stable audio scenes avoids the audioscene from becoming “frozen” during unstable audio scenes in anunnatural way.

Another potential advantage of using the parameters from memory in placeof decoded parameters is that the perceived location of the reproducedsound using the parameters from memory can be closer to the actuallocation of the sound compared to the decoded parameters when a badframe has been indicated.

LISTING OF EMBODIMENTS

1. A method of replacing decoded parameters in a received multichannelsignal, the method comprising:

decoding (900) multichannel parameters of a frame of the receivedmultichannel signal;

determining (902) whether a bad frame is indicated;

responsive to the bad frame being indicated, performing (904) packetloss concealment operations;

responsive to the bad frame not being indicated:

-   -   determining (906), based on at least a coding mode and a        previous bad frame indicator, whether a parameter memory is        corrupted;    -   deriving (908) a location measure of a reconstructed sound        source based on decoded multichannel parameters;    -   determining (910), based on the location measure, whether the        reconstructed sound source is stable and predominantly        concentrated in a subset of channels of multichannels of the        received multichannel signal;    -   responsive to the location measure of the reconstructed sound        source being concentrated in the subset of channels of the        multichannels and is stable and the parameter memory being        corrupted, activating (912) parameter recovery to replace        decoded multichannel parameters with stored multichannel        parameters.        2. The method of Embodiment 1 wherein the multichannels        comprises two channels and determining (910), based on the        location measure, whether the location measure of the        reconstructed sound source is predominantly concentrated in the        subset of channels of the multichannels comprises determining        (910), based on the location measure, whether the location        measure of the reconstructed sound source is predominantly        concentrated in one of the two channels.        3. The method of any of Embodiments 1-2, wherein the coding mode        comprises one of an absolute coding mode and a predictive coding        mode and wherein determining, based on at least the coding mode        and the previous bad frame indicator, whether the parameter        memory is corrupted comprises determining, based on the coding        mode being the predictive coding mode and the previous bad frame        indicator, whether the parameter memory is corrupted.        4. The method of any of Embodiments 1-3, wherein deriving the        location measure comprises deriving the location measure based        on

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{\overset{\hat{}}{\alpha}}_{b}(m)}}}$

where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m.5. The method of Embodiment 4 wherein determining whether the locationmeasure of the reconstructed sound source is predominantly concentratedin a subset of channels of the multichannels comprises:

determining a low-pass filtered position based on

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where γ is a filter parameter, α(m) is a mean of a reconstructedprediction parameter for frame m and α _(LP)(m) is the low-pass filteredposition;

-   -   determining whether an absolute value of the low-pass filtered        position is above a threshold α _(THR);    -   responsive to the absolute value of the low-pass filtered        position being above the threshold α _(THR), determining that        the location measure of the sound source is predominantly        concentrated in a subset of channels of the multichannels.        6. The method of Embodiment 1, wherein deriving the location        measure comprises deriving the location measure based on

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{{\overset{\hat{}}{\alpha}}_{b}(m)} \cdot {{\overset{˜}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum\limits_{k = k_{{start}{(b)}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{˜}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter {circumflex over (α)}_(b) (m) overall sub-bands for each frame m and N_(bands) is a number of sub-bands inframe m, w_(b)(m) and {tilde over (w)}_(b) (m) are weightingcoefficients, k_(end(b)) is an end of a number of sums, k_(start(b)) isa start of the number of sums and X_({circumflex over (M)})(m, k) is atransformed down-mix signal.7. A method of replacing decoded multichannel parameters with storedmultichannel parameters, the method comprising:

determining (1002) whether a coding mode is an absolute coding mode or apredictive coding mode;

responsive to the coding mode being a predictive coding mode:

-   -   determining (1006) if a memory corrupted flag is set;    -   responsive to the memory corrupted flag being set:        -   determining (1008) whether a reconstructed sound source is a            stable sound source and a location measure of the            reconstructed sound source is predominantly concentrated in            a subset of channels of multichannels of a multichannel            signal being decoded;        -   responsive to the reconstructed sound source being a stable            sound source and the location measure of the reconstructed            sound source being predominantly concentrated in the subset            of the channels of the multichannels, substituting (1010)            decoded multichannel parameters with stored multichannel            parameters;    -   responsive to the memory corrupted flag not being set:        -   analyzing (1012) the location measure of the reconstructed            sound source to update the location measure; and        -   updating (1014) the stored multichannel parameters with the            decoded multichannel parameters.            8. The method of Embodiment 7 wherein the multichannels            comprises two channels and determining whether the location            measure of the reconstructed sound source is predominantly            concentrated in a subset of channels comprises determining            (910) whether the location measure of the reconstructed            sound source is predominantly concentrated in one of the two            channels.            9. The method of any of Embodiments 7-8 further comprising:

responsive to the coding mode being an absolute coding mode, unsetting(1004) the memory corrupted flag.

10. The method of any of Embodiments 7-9 further comprising:

responsive to a bad frame being indicated, setting (1000) the memorycorrupted flag.

11. The method of any of Embodiments 7-10 wherein updating the locationmeasure comprises updating the location measure based on

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum\limits_{b = 0}^{N_{bands} - 1}{{\overset{\hat{}}{\alpha}}_{b}(m)}}}$

where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter â_(b) (m) over all sub-bands for eachframe m and N_(bands) is a number of sub-bands in frame m.12. The method of Embodiment 11 wherein determining whether the locationmeasure of the reconstructed sound source is predominantly concentratedin a subset of channels comprises:

determining a low-pass filtered position based on

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where γ is a filter parameter, α(m) is a mean of a reconstructedprediction parameter for frame m and α _(LP)(m) is the low-pass filteredposition;

determining whether an absolute value of the low-pass filtered positionis above a threshold α _(THR);

responsive to the absolute value of the low-pass filtered position beingabove the threshold α _(THR), determining that the location measure ofthe reconstructed sound source is predominantly concentrated in a subsetof channels.

13. The method of Embodiment 7, wherein deriving the location measurecomprises deriving the location measure based on

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{{\hat{\alpha}}_{b}(m)} \cdot {{\overset{\sim}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum_{k = k_{star{t{(b)}}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{\sim}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m, w_(b)(m) and {tilde over (w)}_(b)(m) are weightingcoefficients, k_(end(b)) is an end of a number of sums, k_(start(b)) isa start of the number of sums and X_({circumflex over (M)})(m, k) is atransformed down-mix signal.14. A decoder (200) for a communication network, the decoder (100)comprising:

a processor (801); and

memory (803) coupled with the processor, wherein the memory comprisesinstructions that when executed by the processor causes the processor toperform operations according to any of Embodiments 1-13.

15. A decoder (200) configured to operate in a communication network,wherein the decoder is adapted to perform according to any ofEmbodiments 1-13.16. A computer program comprising computer-executable instructionsconfigured to cause a device to perform the method according to any oneof Embodiments 1-13, when the computer-executable instructions areexecuted on a processor (801) comprised in the device.17. A computer program product comprising a non-transitorycomputer-readable storage medium (803), the non-transitorycomputer-readable storage medium having computer-executable instructionsconfigured to cause a device to perform the method according to any oneof Embodiments 1-13 when the computer-executable instructions areexecuted on a processor (801) comprised in the device.18. An apparatus configured to substitute decoded parameters withestimated parameters in a received multichannel signal, the apparatuscomprising:

at least one processor (801);

memory (803) communicatively coupled to the processor, said memorycomprising instructions executable by the processor, which cause theprocessor to perform operations comprising:

-   -   decoding (900) multichannel parameters of a frame of the        received multichannel signal using one of an absolute coding        mode or a predictive coding mode;    -   determining (902) whether a bad frame is indicated;    -   responsive to the bad frame being indicated, perform packet loss        concealment operations;    -   responsive to the bad frame not being indicated:        -   determining (906), based on at least a coding mode and a            previous bad frame indicator, whether a parameter memory is            corrupted;        -   deriving (908) a location measure of a reconstructed sound            source based on decoded multichannel parameters;        -   determining (910), based on the location measure, whether            the reconstructed sound source is stable and the location            measure is predominantly concentrated in a subset of            channels of multichannels of the received multichannel            signal;        -   responsive to the reconstructed sound source being stable            and the location measure being predominantly concentrated in            a subset of channels of the multichannels and the parameter            memory being corrupted, activating (912) parameter recovery            to replace decoded multichannel parameters with stored            multichannel parameters.            19. The apparatus of Embodiment 18, wherein the coding mode            comprises one of an absolute coding mode and a predictive            coding mode and wherein determining, based on at least the            coding mode and the previous bad frame indicator, whether            the parameter memory is corrupted comprises determining,            based on the coding mode being the predictive coding mode            and the previous bad frame indicator, whether the parameter            memory is corrupted.            20. The apparatus of any of Embodiments 18-19 wherein the            multichannels comprises two channels and determining (910),            based on the location measure, whether the location measure            of the reconstructed sound source is predominantly            concentrated in the subset of channels of the multichannels            comprises determining (910), based on the location measure,            whether the location measure of the reconstructed sound            source is predominantly concentrated in one of the two            channels.            21. The apparatus of any of Embodiments 18-20, wherein            deriving the location measure comprises deriving the            location measure based on

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{\hat{\alpha}}_{b}(m)}}}$

where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m.22. The apparatus of Embodiment 21 wherein determining whether thereconstructed sound source is predominantly concentrated in the subsetof the channels of the multichannels comprises:

determining a low-pass filtered position in accordance with

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where γ is a filter parameter, α(m) is a mean of a reconstructedprediction parameter for frame m and α _(LP)(m) is the low-pass filteredposition;

determining whether an absolute value of the low-pass filtered positionis above a threshold α _(THR);

responsive to the absolute value of the low-pass filtered position beingabove the threshold α _(THR), determining that the reconstructed soundsource is predominantly concentrated in a subset of channels of themultichannels.

23. The apparatus of Embodiment 18, wherein deriving the locationmeasure comprises deriving the location measure based on

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{{\hat{\alpha}}_{b}(m)} \cdot {{\overset{\sim}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum_{k = k_{star{t{(b)}}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{\sim}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where {circumflex over (α)}(m) is the location measure, which comprisesa weighted mean of a reconstructed prediction parameter {circumflex over(α)}_(b) (m) over all sub-bands for each frame m and N_(bands) is anumber of sub-bands in frame m, w_(b) (m) and {tilde over (w)}_(b) (m)are weighting coefficients, k_(end(b)) is an end of a number of sums,k_(start(b)) is a start of the number of sums andX_({circumflex over (M)})(m, k) is a transformed down-mix signal.24. An apparatus configured to substitute decoded parameters withestimated parameters in a received multichannel signal, the apparatuscomprising:

at least one processor (801);

memory (803) communicatively coupled to the processor, said memorycomprising instructions executable by the processor, which when executedcause the processor to perform operations comprising:

-   -   determining (1002) whether a coding mode is an absolute coding        mode or a predictive coding mode;    -   responsive to the coding mode being a predictive coding mode:        -   determining (1006) if a memory corrupted flag is set;        -   responsive to the memory corrupted flag being set:            -   determining (1008) whether a reconstructed sound source                is a stable sound source and a location measure of the                reconstructed sound source is predominantly concentrated                in a subset of channels of multichannels of the received                multichannel signal;            -   responsive to the reconstructed sound source being a                stable sound source and the location measure of the                reconstructed sound source being predominantly                concentrated in the subset of the channels, substituting                (1010) decoded multichannel parameters with stored                multichannel parameters;    -   responsive to the memory corrupted flag not being set:        -   analyzing (1012) the location measure of the reconstructed            sound source to update the location measure; and        -   updating (1014) the stored multichannel parameters with the            decoded multichannel parameters.            25. The apparatus of Embodiment 24, wherein the memory            comprises further instructions executable by the processor,            which when executed cause the processor to perform            operations comprising:

responsive to the coding mode being an absolute coding mode, unsetting(1004) the memory corrupted flag.

26. The apparatus of Embodiment 24, wherein the memory comprises furtherinstructions executable by the processor, which when executed cause theprocessor to perform operations comprising:

responsive to a bad frame being indicated, setting (1000) the memorycorrupted flag.

27. The apparatus of any of Embodiments 24-26 wherein the multichannelscomprises two channels and determining whether the location measure ofthe reconstructed sound source is predominantly concentrated in a subsetof channels determining (910) whether the location measure of thereconstructed sound source is predominantly concentrated in one of thetwo channels.28. The apparatus of any of Embodiments 24-27 wherein updating thelocation measure comprises updating the location measure based on

${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{\hat{\alpha}}_{b}(m)}}}$

where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m.29. The apparatus of Embodiment 28 wherein determining whether thelocation measure of the reconstructed sound source is predominantlyconcentrated in the subset of channels comprises:

determining a low-pass filtered position based on

${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$

where γ is a filter parameter, α(m) is a mean of a reconstructedprediction parameter for frame m and α _(LP)(m) is the low-pass filteredposition;

determining whether an absolute value of the low-pass filtered positionis above a threshold α _(THR);

responsive to the absolute value of the low-pass filtered position beingabove the threshold α _(THR), determining that the location measure ofthe reconstructed sound source is predominantly concentrated in a subsetof channels.

30. The apparatus of Embodiment 24, wherein deriving the locationmeasure comprises deriving the location measure based on

${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{{\hat{\alpha}}_{b}(m)} \cdot {{\overset{\sim}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum_{k = k_{star{t{(b)}}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{\sim}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$

where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter {circumflex over (α)}_(b) (m) overall sub-bands for each frame m and N_(bands) is a number of sub-bands inframe m, w_(b)(m) and {tilde over (w)}_(b) (m) are weightingcoefficients, k_(end(b)) is an end of a number of sums, k_(start(b)) isa start of the number of sums and X_({circumflex over (M)})(m, k) is atransformed down-mix signal.

Explanations for abbreviations from the above disclosure are providedbelow.

Abbreviation Explanation

BFI Bad Frame Indicator

PREY BFI Previous frame Bad Frame Indicator

DFT Discrete Fourier Transform

LP Linear Prediction

PLC Packet Loss Concealment

ECU Error Concealment Unit

FEC Frame Error Correction/Concealment

MDCT Modified Discrete Cosine Transform

MDST Modified Discrete Sine Transform

MSE Mean Squared Error

ODFT Odd Discrete Fourier Transform

LTP Long Term Predictor

ITD Inter-channel Time Difference

IPD Inter-channel Phase Difference

ILD Inter-channel Level Difference

ICC Inter-channel Coherence

FD Frequency Domain

TD Time Domain

FLC Frame Loss Concealment

Citations for references from the above disclosure are provided below.

[1]. C. Faller, “Parametric multichannel audio coding: synthesis ofcoherence cues,” in IEEE Transactions on Audio, Speech, and LanguageProcessing, vol. 14, no. 1, pp. 299-310, January 2006.

[2]. Breebaart, J., Herre, J., Faller, C., Rödén, J., Myburg, F., Disch,S., . . . & Oomen, W. (2005). “MPEG spatial audio coding/MPEG surround:Overview and current status,” 2005 In Preprint 119th Cony. Aud. Eng.Soc. (No. LCAV-CONF-2005-029).

Further definitions and embodiments are discussed below.

In the above-description of various embodiments of present inventiveconcepts, it is to be understood that the terminology used herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of present inventive concepts. Unless otherwisedefined, all terms (including technical and scientific terms) usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which present inventive concepts belong. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of this specification andthe relevant art and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

When an element is referred to as being “connected”, “coupled”,“responsive”, or variants thereof to another element, it can be directlyconnected, coupled, or responsive to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected”, “directly coupled”, “directly responsive”,or variants thereof to another element, there are no interveningelements present. Like numbers refer to like elements throughout.Furthermore, “coupled”, “connected”, “responsive”, or variants thereofas used herein may include wirelessly coupled, connected, or responsive.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Well-known functions or constructions may not be described indetail for brevity and/or clarity. The term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that although the terms first, second, third, etc.may be used herein to describe various elements/operations, theseelements/operations should not be limited by these terms. These termsare only used to distinguish one element/operation from anotherelement/operation. Thus a first element/operation in some embodimentscould be termed a second element/operation in other embodiments withoutdeparting from the teachings of present inventive concepts. The samereference numerals or the same reference designators denote the same orsimilar elements throughout the specification.

As used herein, the terms “comprise”, “comprising”, “comprises”,“include”, “including”, “includes”, “have”, “has”, “having”, or variantsthereof are open-ended, and include one or more stated features,integers, elements, steps, components or functions but does not precludethe presence or addition of one or more other features, integers,elements, steps, components, functions or groups thereof. Furthermore,as used herein, the common abbreviation “e.g.”, which derives from theLatin phrase “exempli gratia,” may be used to introduce or specify ageneral example or examples of a previously mentioned item, and is notintended to be limiting of such item. The common abbreviation “i.e.”,which derives from the Latin phrase “id est,” may be used to specify aparticular item from a more general recitation.

Example embodiments are described herein with reference to blockdiagrams and/or flowchart illustrations of computer-implemented methods,apparatus (systems and/or devices) and/or computer program products. Itis understood that a block of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by computer programinstructions that are performed by one or more computer circuits. Thesecomputer program instructions may be provided to a processor circuit ofa general purpose computer circuit, special purpose computer circuit,and/or other programmable data processing circuit to produce a machine,such that the instructions, which execute via the processor of thecomputer and/or other programmable data processing apparatus, transformand control transistors, values stored in memory locations, and otherhardware components within such circuitry to implement thefunctions/acts specified in the block diagrams and/or flowchart block orblocks, and thereby create means (functionality) and/or structure forimplementing the functions/acts specified in the block diagrams and/orflowchart block(s).

These computer program instructions may also be stored in a tangiblecomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instructions whichimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks. Accordingly, embodiments of present inventiveconcepts may be embodied in hardware and/or in software (includingfirmware, resident software, micro-code, etc.) that runs on a processorsuch as a digital signal processor, which may collectively be referredto as “circuitry,” “a module” or variants thereof.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated, and/orblocks/operations may be omitted without departing from the scope ofinventive concepts. Moreover, although some of the diagrams includearrows on communication paths to show a primary direction ofcommunication, it is to be understood that communication may occur inthe opposite direction to the depicted arrows.

Many variations and modifications can be made to the embodiments withoutsubstantially departing from the principles of the present inventiveconcepts. All such variations and modifications are intended to beincluded herein within the scope of present inventive concepts.Accordingly, the above disclosed subject matter is to be consideredillustrative, and not restrictive, and the examples of embodiments areintended to cover all such modifications, enhancements, and otherembodiments, which fall within the spirit and scope of present inventiveconcepts. Thus, to the maximum extent allowed by law, the scope ofpresent inventive concepts are to be determined by the broadestpermissible interpretation of the present disclosure including theexamples of embodiments and their equivalents, and shall not berestricted or limited by the foregoing detailed description.

Generally, all terms used herein are to be interpreted according totheir ordinary meaning in the relevant technical field, unless adifferent meaning is clearly given and/or is implied from the context inwhich it is used. All references to a/an/the element, apparatus,component, means, step, etc. are to be interpreted openly as referringto at least one instance of the element, apparatus, component, means,step, etc., unless explicitly stated otherwise. The steps of any methodsdisclosed herein do not have to be performed in the exact orderdisclosed, unless a step is explicitly described as following orpreceding another step and/or where it is implicit that a step mustfollow or precede another step. Any feature of any of the embodimentsdisclosed herein may be applied to any other embodiment, whereverappropriate. Likewise, any advantage of any of the embodiments may applyto any other embodiments, and vice versa.

Any appropriate steps, methods, features, functions, or benefitsdisclosed herein may be performed through one or more functional unitsor modules of one or more virtual apparatuses. Each virtual apparatusmay comprise a number of these functional units. These functional unitsmay be implemented via processing circuitry, which may include one ormore microprocessor or microcontrollers, as well as other digitalhardware, which may include digital signal processors (DSPs),special-purpose digital logic, and the like. The processing circuitrymay be configured to execute program code stored in memory, which mayinclude one or several types of memory such as read-only memory (ROM),random-access memory (RAM), cache memory, flash memory devices, opticalstorage devices, etc. Program code stored in memory includes programinstructions for executing one or more telecommunications and/or datacommunications protocols as well as instructions for carrying out one ormore of the techniques described herein. In some implementations, theprocessing circuitry may be used to cause the respective functional unitto perform corresponding functions according one or more embodiments ofthe present disclosure.

1. A method of replacing decoded parameters in a received multichannelsignal, the method comprising: decoding multichannel parameters of aframe of the received multichannel signal; determining whether a badframe is indicated; responsive to the bad frame being indicated,determining that a parameter memory is corrupted; responsive to the badframe not being indicated: responsive to the parameter memory not beingcorrupted, deriving a location measure of a reconstructed sound sourcebased on decoded multichannel parameters; responsive to the parametermemory being corrupted, determining, based on the location measure,whether the reconstructed sound source is stable and predominantlyconcentrated in a subset of channels of multichannels of the receivedmultichannel signal; and responsive to the reconstructed sound sourcebeing concentrated in the subset of channels of the multichannels andbeing stable, activating parameter recovery to replace decodedmultichannel parameters with stored multichannel parameters.
 2. Themethod of claim 1, further in response to the bad frame being indicated,performing packet loss concealment operations.
 3. The method of claim 1,further in response to the bad frame not being indicated, storing thedecoded multichannel parameters as the stored multichannel parameters.4. The method of claim 1 wherein the multichannels comprises twochannels and determining, based on the location measure, whether thelocation measure of the reconstructed sound source is predominantlyconcentrated in the subset of channels of the multichannels comprisesdetermining, based on the location measure, whether the location measureof the reconstructed sound source is predominantly concentrated in oneof the two channels.
 5. The method of claim 1, wherein a coding modecomprises one of an absolute coding mode and a predictive coding modeand responsive to the coding mode being the absolute coding mode,unsetting a memory corrupted flag responsive to the memory corruptedflag being set.
 6. The method of claim 1, wherein deriving the locationmeasure comprises deriving the location measure based on${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{\hat{\alpha}}_{b}(m)}}}$where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m.
 7. The method of claim 6 wherein determining whether thelocation measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels of the multichannels comprises:determining a low-pass filtered position based on${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$ where γ is a filter parameter, α(m) is a mean of areconstructed prediction parameter for frame in and α _(LP)(m) is thelow-pass filtered position; determining whether an absolute value of thelow-pass filtered position is above a threshold α _(THR); and responsiveto the absolute value of the low-pass filtered position being above thethreshold α _(THR), determining that the location measure of the soundsource is predominantly concentrated in a subset of channels of themultichannels.
 8. The method of claim 1, wherein deriving the locationmeasure comprises deriving the location measure based on${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{{\hat{\alpha}}_{b}(m)} \cdot {{\overset{\sim}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum_{k = k_{star{t{(b)}}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{\sim}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter ā_(b) (m) over all sub-bands for eachframe m and N_(bands) is a number of sub-bands in frame m, w_(b)(m) and{tilde over (w)}^(b)(m) are weighting coefficients, k_(end(b)) is an endof a number of sums, k_(start(b)) is a start of the number of sums andX_({circumflex over (M)})(m, k) is a transformed down-mix signal.
 9. Adecoder for a communication network, the decoder comprising: aprocessor; and memory coupled with the processor, wherein the memorycomprises instructions that when executed by the processor causes theprocessor to perform operations comprising: decoding multichannelparameters of a frame of a received multichannel signal; determiningwhether a bad frame is indicated; responsive to the bad frame beingindicated, determining that a parameter memory is corrupted; responsiveto the bad frame not being indicated: responsive to the parameter memorynot being corrupted, deriving a location measure of a reconstructedsound source based on decoded multichannel parameters; responsive to theparameter memory being corrupted, determining based on the locationmeasure, whether the reconstructed sound source is stable andpredominantly concentrated in a subset of channels of multichannels ofthe received multichannel signal; and responsive to the reconstructedsound source being concentrated in the subset of channels of themultichannels and being stable, activating parameter recovery to replacedecoded multichannel parameters with stored multichannel parameters. 10.The decoder of claim 9 wherein the multichannels comprises two channelsand determining, based on the location measure, whether the locationmeasure of the reconstructed sound source is predominantly concentratedin the subset of channels of the multichannels comprises determining,based on the location measure, whether the location measure of thereconstructed sound source is predominantly concentrated in one of thetwo channels.
 11. The decoder of claim 9, wherein the coding modecomprises one of an absolute coding mode and a predictive coding modeand responsive to the coding mode being the absolute coding mode,unsetting a memory corrupted flag responsive to the memory corruptedflag being set.
 12. The decoder of claim 9, wherein deriving thelocation measure comprises deriving the location measure based on${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{\hat{\alpha}}_{b}(m)}}}$where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m.
 13. The decoder of claim 12 wherein determining whether thelocation measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels of the multichannels comprises:determining a low-pass filtered position based on${{\overset{\_}{\alpha}}_{LP}(m)} = \left\{ \begin{matrix}{{{\gamma{\overset{\_}{\alpha}(m)}} + {\left( {1 - \gamma} \right){{\overset{\_}{\alpha}}_{LP}\left( {m - 1} \right)}}},} & {{{\overset{\_}{\alpha}(m)}} > {\overset{\_}{\alpha}}_{THR}} \\{0,} & {otherwise}\end{matrix} \right.$ where γ is a filter parameter, α(m) is a mean of areconstructed prediction parameter for frame m and α _(LP)(m) is thelow-pass filtered position; determining whether an absolute value of thelow-pass filtered position is above a threshold α _(THR); and responsiveto the absolute value of the low-pass filtered position being above thethreshold α _(THR), determining that the location measure of the soundsource is predominantly concentrated in a subset of channels of themultichannels.
 14. The decoder of claim 13, wherein deriving thelocation measure comprises deriving the location measure based on${{\overset{\_}{\alpha}}_{w}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{{\hat{\alpha}}_{b}(m)} \cdot {{\overset{\sim}{w}}_{b}(m)}}}}$${w_{b}(m)} = {\frac{1}{k_{{end}{(b)}} - k_{star{t{(b)}}} + 1}{\sum_{k = k_{star{t{(b)}}}}^{k_{en{d{(b)}}}}{X_{\hat{M}}\left( {m,k} \right)}^{2}}}$${{\overset{\sim}{w}}_{b}(m)} = \frac{{w_{b}(m)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}{{\max\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)} - {\min\left( {w_{{0\mspace{14mu}\ldots\mspace{14mu} N_{bands}} - 1}(m)} \right)}}$where α(m) is the location measure, which comprises a weighted mean of areconstructed prediction parameter {circumflex over (α)}_(b) (m) overall sub-bands for each frame m and N_(bands) is a number of sub-bands inframe m, w_(b)(m) and {tilde over (w)}_(b)(m) are weightingcoefficients, k_(end(b)) is an end of a number of sums, k_(start(b)) isa start of the number of sums and X_({circumflex over (M)})(m, k) is atransformed down-mix signal. 15.-18. (canceled)
 19. A computer programproduct comprising a non-transitory computer-readable storage medium,the non-transitory computer-readable storage medium havingcomputer-executable instructions that when executed on a processorcomprised in device cause the device to perform operations comprising:decoding multichannel parameters of a frame of a received multichannelsignal; determining whether a bad frame is indicated; responsive to thebad frame being indicated, determining that a parameter memory iscorrupted; responsive to the bad frame not being indicated: responsiveto the parameter memory not being corrupted, deriving a location measureof a reconstructed sound source based on decoded multichannelparameters; responsive to the parameter memory being corrupted,determining, based on the location measure, whether the reconstructedsound source is stable and predominantly concentrated in a subset ofchannels of multichannels of the received multichannel signal; andresponsive to the reconstructed sound source being concentrated in thesubset of channels of the multichannels and being stable, activatingparameter recovery to replace decoded multichannel parameters withstored multichannel parameters.
 20. (canceled)
 21. A method of replacingdecoded multichannel parameters with stored multichannel parameters, themethod comprising: determining whether a coding mode is an absolutecoding mode or a predictive coding mode; responsive to the coding modebeing a predictive coding mode: determining if a memory corrupted flagis set; responsive to the memory corrupted flag being set: determiningwhether a reconstructed sound source is a stable sound source and alocation measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels of multichannels of a multichannelsignal being decoded; responsive to the reconstructed sound source beinga stable sound source and the location measure of the reconstructedsound source being predominantly concentrated in the subset of thechannels of the multichannels, substituting decoded multichannelparameters with stored multichannel parameters; and responsive to thememory corrupted flag not being set: analyzing the location measure ofthe reconstructed sound source to update the location measure; andupdating the stored multichannel parameters with the decodedmultichannel parameters.
 22. The method of claim 21 wherein themultichannels comprises two channels and determining whether thelocation measure of the reconstructed sound source is predominantlyconcentrated in a subset of channels comprises determining whether thelocation measure of the reconstructed sound source is predominantlyconcentrated in one of the two channels.
 23. The method of claim 21further comprising: responsive to the coding mode being an absolutecoding mode, unsetting the memory corrupted flag.
 24. The method ofclaim 21 further comprising: responsive to a bad frame being indicated,setting the memory corrupted flag.
 25. The method of claim 21 furthercomprising updating the location measure based on${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{\hat{\alpha}}_{b}(m)}}}$where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b)(m) over allsub-bands for each frame m and N_(bands) is a number of sub-bands inframe m. 26.-27. (canceled)
 28. A decoder for a communication network,the decoder comprising: a processor; and memory coupled with theprocessor, wherein the memory comprises instructions that when executedby the processor causes the processor to perform operations comprising:determining whether a coding mode is an absolute coding mode or apredictive coding mode; responsive to the coding mode being a predictivecoding mode: determining if a memory corrupted flag is set; responsiveto the memory corrupted flag being set: determining whether areconstructed sound source is a stable sound source and a locationmeasure of the reconstructed sound source is predominantly concentratedin a subset of channels of multichannels of a multichannel signal beingdecoded; responsive to the reconstructed sound source being a stablesound source and the location measure of the reconstructed sound sourcebeing predominantly concentrated in the subset of the channels of themultichannels, substituting decoded multichannel parameters with storedmultichannel parameters; and responsive to the memory corrupted flag notbeing set: analyzing the location measure of the reconstructed soundsource to update the location measure; and updating the storedmultichannel parameters with the decoded multichannel parameters. 29.The decoder of claim 28 wherein the multichannels comprises two channelsand determining whether the location measure of the reconstructed soundsource is predominantly concentrated in a subset of channels comprisesdetermining whether the location measure of the reconstructed soundsource is predominantly concentrated in one of the two channels.
 30. Thedecoder of claim 28, wherein the memory comprises further instructionsthat when executed by the processor causes the processor to performfurther operations comprising: responsive to the coding mode being anabsolute coding mode, unsetting the memory corrupted flag.
 31. Thedecoder of claim 28 wherein the memory comprises further instructionsthat when executed by the processor causes the processor to performfurther operations comprising: responsive to a bad frame beingindicated, setting the memory corrupted flag.
 32. The decoder of claim28 wherein the memory comprises further instructions that when executedby the processor causes the processor to perform further operationscomprising updating the location measure based on${\overset{\_}{\alpha}(m)} = {\frac{1}{N_{bands}}{\sum_{b = 0}^{N_{bands} - 1}{{\hat{\alpha}}_{b}(m)}}}$where α(m) is the location measure, which comprises a mean of areconstructed prediction parameter {circumflex over (α)}_(b) (m) overall sub-bands for each frame m and N_(bands) is a number of sub-bands inframe m. 33.-38. (canceled)
 39. A computer program product comprising anon-transitory computer-readable storage medium, the non-transitorycomputer-readable storage medium having computer-executable instructionsthat when executed on a processor comprised in device cause the deviceto perform operations comprising: determining whether a coding mode isan absolute coding mode or a predictive coding mode; responsive to thecoding mode being a predictive coding mode: determining if a memorycorrupted flag is set; responsive to the memory corrupted flag beingset: determining whether a reconstructed sound source is a stable soundsource and a location measure of the reconstructed sound source ispredominantly concentrated in a subset of channels of multichannels of amultichannel signal being decoded; responsive to the reconstructed soundsource being a stable sound source and the location measure of thereconstructed sound source being predominantly concentrated in thesubset of the channels of the multichannels, substituting decodedmultichannel parameters with stored multichannel parameters; andresponsive to the memory corrupted flag not being set: analyzing thelocation measure of the reconstructed sound source to update thelocation measure; and updating the stored multichannel parameters withthe decoded multichannel parameters. 40.-53. (canceled)